multiples = [i for i in range(30) if i%3 is 0]
print(multiples)

print("字典推导式")
mcase = {'a':10, 'b':34, 'A':7, 'Z':3}
mcase_frequency = {
    k.lower(): mcase.get(k.lower(), 0) + mcase.get(k.upper(), 0)
    for k in mcase.keys()
}
print(mcase_frequency)

print("快速对换键和值")
{v:k for k,v in multiples.item()}
